1. Field of the Invention
The present invention relates to a paper feed unit and an image forming apparatus, e.g., an electronic copying machine or a laser printer, to which the paper feed unit is mounted.
2. Description of the Related Art
An electronic copying machine has a paper feed unit mounted on it. A conventional paper feed unit stores copying paper (to be referred to as paper hereinafter) of only one size. U.S. Pat. No. 4,953,844 discloses an electronic copying machine capable of copying on paper of a plurality of sizes, a plurality of paper feed cassettes corresponding in number to the paper sizes are mounted all at once, or are exchangeably mounted one at a time. Since a plurality of paper feed units are used, the cost is increased. The paper feed cassettes must be exchanged in accordance with the sizes of the paper to be used, requiring a cumbersome paper feed operation. An extra space is required to store paper feed cassettes which are not currently used. Furthermore, although paper sheets of different sizes are used at different frequencies, the conventional paper feed cassettes have the same size to store the same number of paper sheets in order to facilitate mounting of the cassettes to the electronic copying machine. Therefore, paper of a frequently used size must be replenished often.